Article gripping system for lift trucks



Mavy 13, 1952 J, A, FRISCHM'ANN 2,596,895

ARTICLE GRIPPING SYSTEM FOR LIFT TRUCKS Filed-NOV. 18, 1948 INVEN TOR. JOSEPH. A- FE/SCHMANN A TTOPNEYS Patented May 13, 1952 ARTICLE GRIPPING SYSTEM FOR LIFT TRUCKS Joseph A. Frischmann, Cleveland, Ohio, assigner to Towmotor Corporation, Cleveland, Ohio, a

corporation of Ohio Application November'l, 1948, Serial No. 60,726

6 Claims.

This invention relates to the art of material handling and in its preferred embodiment is directed to an improved system for handling articles finding particular application in lift trucks and the like. The preferred embodiment of the invention described herein comprises means for gripping a load to be elevated and transported by a lift truck and a novel and improved hydraulic system for the actuation of the gripping means.

Although the preferred embodiment of the invention is in a lift truck, it will be apparent to those skilled in the material handling art from the description of the invention that it is adaptable to other environments and that the hydraulic system of the invention has a wide field of beneficial employment.

Considering, by way of illustration, a specific problem to the solution of which the invention has been directed and the advantages of the invention in relation thereto, it is well known that the conventional manner of lifting articles such as boxes, barrels, paper rolls, and the like with a lift truck has involved thrusting a fork or plate extending horizont-ally from the carriage of the lift truck beneath the load to support the load on the projecting fork or plate of the lift truck. This method of handling articles has certain deficiencies, among them being that it often, as a practical matter, requires the use of pallets to support the load above the floor or considerable maneuvering of the lift truck to get the fork or the like beneath the load. In connection with the handling of paper rolls, for example, a method which has been proposed involves thrusting a flat plate or blade beneath the roll which is standing on end and rotating the carriage to support the roll in a horizontal position on forks or an apron. This method is not adapted to handling rolls stacked or to be stacked endon-end.

In using the prior system, considerable care and skill/QI the operator of the lift truck is required -tof et the blade under the roll of paper without d l" aging the roll, and the somewhat delicatem l :euvering involved is time-consuming.

tBecausevof this fact, attempts have been made to'eiimniat the uiting made and hamue the entirely with the gripping jaws. The esults'have not been entirely satisfactory, how- VBLbBQauSe the hydraulically actuated clamping Ws' would relax their grip as a result of slow l lakage I oil ,3and in time would become so loose 'I'he advantages of eliminating the blade are Preciable. The advantages of retaining the aulc system for actuating the gripping de- Vi V vare also very great, since lift trucks are eq x D'Ped with hydraulic power systems to actuate not; O-nly the gripping jaws but to lift the car- Cil riage on the mast, to tilt the mast, and sometimes for other purposes. such as upending. See, for example, the Lehmann et al. Patent No. 2,281,- 004, April 28, 1942.

The problem outlined above is solved by this invention, which retains the hydraulic system and its advantages, and which imparts to the hydraulic system the ability to retain its grip on a non-compressible load. 'I'he invention'is based on the conception that the deiiciencies of the hydraulic system could be overcome by the provision of a valve to substantially prevent loss of fluid from the cylinder to the hydraulic supply system therefor and an accumulator to maintain the pressure in the cylinder despite any remaining leakage.

As a result of the invention, the lift truck may be readily and easily adapted to handle loads by gripping them between opposed hydraulically actuated jaws, without any need for a supporting fork or platform beneath the load. The handling of many classes of articles is thus expedited and the eld of usefulness of lift trucks is thus enlarged.

The principal object of the invention is to improve the handling of objects such as, for example, rolls of paper, oil drums, sewer tile, barrels, and boxes.

Another object of the invention is to provide a hydraulically actuated device capable of gripping substantially non-compressible objects and retaining a tight grip thereon.

Another object of the invention is to provide a holding device readily adaptable to installation in existing hydraulic power systems and which will be effective to eliminate creeping of the piston under load.

Other objects and advantages, more or less ancillary to the foregoing, and the manner in which all the various objects are realized will appear in the following description, which, considered in connection with the accompanying drawings, sets forth the preferred embodiment of the invention.

The drawing illustrates the holding device of the invention, in a sectional view in schematic circuit relation to the other elements of the hydraulic power system and the gripping device, the elements other than the holding device being illustrated conventionally.

The invention is independent of the general constructional features of the lift truck. In its preferred embodiment it has been incorporated in Towmotor lift trucks. Since lift trucks in which this invention may be incorporated are well known to those skilled in the art, and the details of the truck are immaterial to an understanding of the invention, the lift truck is not described or illustrated herein.. The abovementioned Lehmann et al. patent discloses a lift truck of the character to which reference is made herein.

Referring to the drawing: The principal elements of the system are a reservoir R for hydraulic fluid, a pump P, a manual control valve V, a gripping device G which is shown holding a load L which is illustrated as a roll of paper, a hydraulic motor for effecting the gripping operation, the motor being illustrated herein as a double-acting cylinder,^and a holding device H which combineswith the other elements of the system to effectuate the benec'ial results outlined above.

Inasmuch as the reservoir, pump, valve, and motor are conventional elements well known and readily obtainable commercially, the details of which are not relevant to an understanding of the invention, they are illustrated schematically and will not require detailed description.

The invention which is disclosed and claimed herein does not depend upon the specific structure of the gripping device G, and, for this reason, it is considered that the invention may be described with greatest clarity and conciseness by the utilization of a simplified schematic drawing of the gripping device, which is to be taken as generally illustrative of the type of structure involved. The specic form of the .gripping device is optional, and, in practice, dependent upon the dimensions of the carriage, the proportions of the articles to be handled, and other considerations such as the presence or absence of upending mechanisms.

As illustrated schematically herein, the gripping device is mounted on the carriage I8 of a lift truck, which carriage is movable vertically on a mast (not shown). The gripping device includes a xed arm I9 with a. pad or jaw 20 at the end thereof, and an arm 2I pivoted at 22 to the carriage and with a pad or jaw 23 opposable to the jaw 20. The double-acting hydraulic cylinder M is pivoted at 24 to the xed arm and the piston rod of the piston 26 is articulated at 25 to the movable arm. The conduits I4 and I5 by which the cylinder M is supplied may, of course, involve any suitable arrangement for flexibility to accommodate vertical, lateral. or rotational movement of the carriage as necessary.

By way of preamble to the description of the invention, we may consider the operation of the system, omitting the functions of the holding device H, as if the holding device were merely a means to couple the conduits I3 and I5 leading from the manual control valve V to the motor M.

A hydraulic fluid is drawn from the reservoir R through a conduit I by the 'pump P, which may be driven by any convenient prime .mover (not shown) and is delivered bythe pump under pressure through a conduit I-I into the -manual control valve V. In practice, .such a valve may be a multiple valve adapted to control a number of cylinders, but the .control of additional cylinders is likewise immaterial to the present invention, and the valve V may be a single valve. The valve V is controlled by the operating handle 9, which may be set to three positions. In the hold position of the valve the pump is bypassed through a line I2 to the reservoir and the conduits I3 and I4 by which the valve is coupled to the cylinder are blocked. In the close" position of the handle, uid from the Dump iS di rected to one end of the .motor M through the conduits I3 and I5 and fluid exhausted-from the cylinder through the conduit I4 is directed into the reservoir conduit I2. The piston 26 is thus driven in the direction to close the gripping jaws. In the iopen position of the valve the conduit-s I I and I# are interconnected and the conduits I3 and I2 are interconnected to operate the piston and jaws in the opposite direction. Valves for this .purpose .are well known and commercially available, and therefore detailed description of the valve is unnecessary.

When the valve V is operated to close the jaws and is .then moved to its hold position, iluid will be locked in the cylinder and the load will be Aheld in a tight grip. However, in order to secure free operation of the manual control valve, the clearances are such that some leakage of oil will occur through this valve. Leakage may also occur 'past the piston 26 and, in some types of installations, around `the piston rod. Assuming that the 'load is only slightly compressible and the gripping device -is reasonably rigid, as it no1'- mally would be, ,only avery slight leakage of oil is necessary 'to reduce the pressure to a value low :enough that the load can slip from the gripping device. It :is :not practicable to leave the manual .control `valve :in close position to keep pump pressure in the cylinder continuously, as

this closes the bypass at the valve and requires the pump to operate against full pressure, the pump discharge being passed through a relief valve. 'This results in undue wear of the pump,

- undue heating of the oil. excessive noise, and a great waste of power, and is thus unacceptable. These disadvantages, as well as the relaxation of the grip on the articles referred to above, are

avoided 'by 'the incorporation of the holding device H.

In its preferred form, the holding device.H comprises -a body 3U which may be a generally rectangular block formed with tapped connections 3I and 32 respectively for the conduits I3 and I'5 by which the device H is interposed in the -uid conduit from the manual control valve to the closing end of the cylinder. The valve block also is 'bored and tapped to provide a connection'33 for abranch Ida of the uid line leading to the end of the cylinder which opens the Jaws.

The exterior ports 3I and 32 are interconnected 'by bores 'in the valve body which form a continuouspassage in which is located a check valve. The inlet connection 3| intersects a bore 34 which extends through the valve block and which in turn intersects a bore 35 which opens into the outlet port 32. The bore 34 is counterbored to provide a shoulder against which an annular seat 36 of the check valve is pressed. The movable member of the check valve is preferably a sphere 31 guided'within a central bore 38 in a retainer plug 39 threaded into place in the outer end of the bore 34.' Acoil spring 40 seated in the chamber 3-8 normally urges the ball 31 against the seat 36. As will be apparent, flow of iiuid from the port 3I to the port 32 may proceed through the check valve without any significant hindrance, but an excess -of pressure in the connection- I32 over that in the connection 3I presses the valve ball in the seat to prevent iiow in the reverse direction.- Thus, insofar as the check valve alone is concerned, the greater the pressuretending to cause leakage back into the manual 6011131101 valve, the more rmly the ball is seated" t0 Prevent such'leakage.

-In -order to permit -release of the loadl When desired, the ball 81 must be unseated by means capable of overcoming the pressure of theiball against its seat. This is preferably accomplished n LJy a snap 'ring 63.

by a piston or plunger 42 which is reciprocable in a portion of the bore 34 constituting a cylinder for the plunger. A plug 43 threaded into the valve block serves as a cylinder head and as a stop to limit movement of the plunger 42. The bore 34 is recessed slightly, as indicated at 44, to form an inlet chamber above the piston or plunger 42 to which fluid is admitted through a constricted passage 46 from the external port 33. 'I'he plunger 42 bears a reduced extension 41 which extends through the central opening of the valve seat 36 into the vicinity of the ball 31.

When the manual control valve V is operated to connect the pump through the conduit I4 to the opening end of the motor M, the conduit I3 is connected to the reservoir line I2. Pressure in the conduit I4 is communicated through the conduit I4a, inlet port 43, and passage 46 into the chamber 44 above the plunger 42, which is thereby forced downwardly, forcing the valve ball` 31 from the seat to permit return flow of fluid from the cylinder and opening of the jaws. Downward movement of the plunger 42 is limited by a shoulder 48 in the bore.

When the manual valve is shifted to again close the jaws, fluid under pressure entering the port 3| bears against the undersurface of the plunger 42 to return it to the position illustrated in the drawing, forcing the fluid above the piston into vthe lines I 4a, I4, and to the exhaust line I2. As a result. the ball 31 seats under the action of the spring 39 and the pressure in the conduit I5 as soon as the valve is returned to its hold" position.

'I'he holding device of the invention includes an accumulator of a type particularly suited for the purpose of the invention. which requires maintenance of pressure but does not necessitate the accumulation of any substantial volume of fluid for that purpose since the purpose is to maintain a static head. The accumulator comprises a plunger 50 reciprocable in a bore 5I in the block 30, which is recessed as indicated at 52 to provide an inlet chamber. The inner end of the bore 35 is connected through a restricted oriiice 53 with the chamber 52 so that the cylinder 5I is always in communication with the line I5. The upper end of the cylinder 5I is counterbored in two steps to provide a seat for a packing retaining ring 54 which is of annular form and is retained against the upper shoulder 55. The lower face of the ring 54 is formed with an annular extension 56 which closely approaches the bottom of the counterbore. 'I'he ring 56 defines annular spaces within which are disposed sealing rings 51 and 58 which may be of the type known commerciallygas O-rings. The inner O-ring 58 seals A,against escape of fluid along the cylinder wall and the outer O-ring 51 seals against escape of fluid along the outer surface of the packing ring 54.

l A washer 6I is retained on a central boss 62 projecting' from the upper end of the plunger 50 The washer 6I normally bears against the upper surface of the ring 54 to provide sa limit stop for downward movement of the plungegr and provides a seat for a strong compression SI1-ring 54 which urges the plunger 50 into the cyliI-ider 5I. The spring 64 is preferably contained iin a tube 66 which is inserted in the upper counterfuore s1 of the cylinder bore 5|, resting against; the packing ring 54. The upper end of the spllng 54 and tube 68 abut against a cap 68 which is formed with a central boss 69 tting withinthb tube 6G. The cap 68 is retained in position by bolts 1I passing through the head and 6 received in tapped holes 12 in the valve block 3U.

A stop plug 13 for the piston 50 extends downwardly from the cap 68 within the spring 64. being secured to the cap by a socket-headed machine screw 14. 'Ihe upper part of the valve H has been broken in the drawing to conserve space; the spring 64 is preferably somewhat longer than illustrated. The spring is preferably of a length approximately three times the stroke of the piston 50 to provide a desirable approximation to constancy of pressure throughout the stroke of the plunger 50 and to avoid undue compression of the spring.

The outer end of the passage 35 is closed by a plug 8l. Gaskets 82 and 83 may be provided under the heads of the plugs 39 and 43, respectively. Transverse bores 84 may be provided in the valve block for mounting bolts for the assembly.

Considering now the operation of the accumulator, when the manual valve V is operated to close the jaws G, fluid passing through the line I3, the check valve 31, and passage 35 is conducted through the orifice 53 into the chamber 52, applying pressure to the lower surface of the plunger 50. However, as long as the arm 2| is swinging into engagement with the load, the pressure in the chamber 35 is low and the piston 50 is not displaced. When the arm 2| moves to the point at which the load is clamped between the jaws 23 and 20, the pressure rapidly builds up and becomes suilicient to overcome the force of the spring S4. The plunger 50 is forced upward into contact with the stop 13, thus charging the cylinder 5I with oil under pressure. The restricted orifice 53 is desirable to prevent too rapid ow into the cylinder 5I which would cause the plunger 5U to strike the stop 13 with undesirably high velocity.

It is, of course, possible that the manual valve V could be closed with the plunger 5U in an intermediate position, but this is unlikely in view of the relatively small size of the cylinder 5I. When the plunger 50 engages the stop, the usual relief valve of the hydraulic system will operate, evidencing the fact that the system is full of oil at full system pressure. The valve V is then returned to its hold position, whereupon the check valve 31 seats and is held seated by the pressure in the cylinders M and 5I. If there should be any lessening of pressure in the system due to leakage, or to a slight inward yielding of the load, the spring 64 will force the plunger 50 inward to displace fluid from the cylinder 5I into the motor M to maintain a firm grip on the load L. The displacement of the plunger 50 need not ordinarily be large. For the installation described, a displacement of a cubic inch or two is considered to be adequate to hold for long periods of time.

When the manual valve V is actuated to release the load, the spring 54 displaces the fluid from the cylinder 5I, the restricted Outlet 53 serving at this time to prevent the washer 6I from being driven too vigorously against the ring 54.

While the preferred form of motor is a doubleacting type and preferably a double-acting cylinder as illustrated, other types of double-acting motors may be substituted, or a single-acting motor such as a. single-acting cylinder may be employed if desired. The substitution of a single-acting cylinder for the double-acting cylinder illustrated involves merely the elimination of the connection of the conduit I4 to the 7 Cylinder. .The connection of the line Ma into the holding device H is necessary as before to release the check valve to permit outflow of fluid from the line l5.

The motor M and the arrangement of the movable arm 2| could be modied so that the rod end of the cylinder is filled to close the jaws. This arrangement is believed to be less desirable because o f the probability of leakage around the piston rod fand the lower eii'ective piston area.

Although :the foregoing description is necessarily of a detailed character, in order that the invention may be completely set forth, .it is to be nunderstood that the specic terminology is not intended to be restrictive or confining, and that various rearrangements of parts and modifications of .detail may be resorted to without departing from the .scope or vspirit of the invention as herein claimed.

Iolaim:

4l. In a lift truclg, -a load-supporting carriage, means thereon to grip ,a load, a hydraulic motor actuatable to close the gripping means on a load and retain the same in closed condition, a source of uid under pressure, a manual control valve movable to effect ow of fluid from `the source through a conduit .'co the motor to grip the load and .movable to effect ow from the motor through the conduit to -release the load; in combination with a holding device comprising a. check valve in the conduit disposed to prevent ow from the motor, means for unseating the check valve operated by movement of the manual control valve to release the load, a cylinder, a. spring-loaded piston therein, a restricted fluid connection between the cylinder and the conduit between the check valve and motor, and a positive stop for the piston.

2. In a lift truck, a load-supporting carriage, means thereon to grip a load, a hydraulic motor actuatable to close the gripping means on a load and retain the same in closed condition, a source of iiuid under pressure, a manual control valve movable -to effect flow of iluid from the source through a conduit to the motor to grip the load and movable to effect flow vfrom the motor through the .conduit to release the load;.in combination with a holding device comprising a check 4valve in the conduit disposed to prevent now from .the motor, means for unseating the check valve operated by -movement of the manual control valve to release the load, a cylinder, a spring-loaded piston therein, a constantly open fluid connection between the cylinder and the motor, and a positive stop for the piston.

3. In a lift truck, a load-supporting carriage, means thereon 'to grip a load, a hydraulic motor actuatable to close the vgripping means on a load and retain the same in closed condition, a source of fluid under pressure, a manual control valve movable .to effect flow .of fluid from the source through a conduit to the motor to grip the load and movable to eiect ow from the motor through the conduitto release the load; in combination with a holding device comprising a. check valve in the conduit disposed to prevent flow from the motor, means for unseating the check valve .operated by movement of the manual control valve to release the load, a cylinder, a spring-loaded piston therein, and a. restricted fluid connection between the cylinder and the conduit between the check valve and motor.

4. vIn a 4lift truck, a load-supporting carriage, means thereon to grip a load, a 'hydraulic motor actuatable :to close the gripping means on a load and retain the same in closed condition, a source of iluid under pressure, a manual control valve movable to eiect flow of uid from the source through a conduit to the motor to grip the load and movable to effect flow from the motor through the conduit to release the load; in combination with a holding device comprising a check valve in the conduit disposed to prevent ow from the motor. means for unseating the check valve operated b y movement of the manual control valve to release the load comprising a cylinder, a plunger therein engageable with the check valve. means operable by movement of the manual .control .valve to load-releasing position to direct fluid .under pressure into the cylinder to open the check valve; and a spring-loaded plunger constantly o pen to the conduit between the check valve and motor.

5. In combination, a load-supporting carriage adapted to b e mounted on a lift truck, means onsaidcarriage .to grip a load, a hydraulic motor actuatable to close the gripping means on a load and retain the same in closed condition, a source of uid under pressure, a .conduit between said source and motor, a manual control valve in said conduit movable to e'ect now of uid from the source through said conduit to the motor to grip the load and movable to effect flow from the motor through the ,conduit xto release the load, a. load holding device comprising a check valve in the conduit .disposed to prevent ow from the motor, means for unseating .the check valve operated by Amovement ,of the manual control valve to release the loa-d, a cylinder, a spring-loaded piston therein. .and .a fluid connection between the cylinder and that part of the conduit disposed between the .check -valve and motor.

6. In combination, .a load-supporting carriage adapted to be mounted on a lift truck, means on said carriage to grip a load, a hydraulic motor actuatable to close the gripping means on a load and retain the same in closed condition, a source of fluid under pressure, a conduit between said source and motor, a manual control valve in said conduit movable to effect flow of fluid from the source through said conduit to the motor to grip the load and movable to effect nov.l from the motor through the conduit to release the load, a load-holding device comprising a check valve in the conduit disposed to prevent flow from the motor, a plunger for unseating the check valve, a second conduit between said valve and plunger, said plunger being operated to unseat said check valve upon movement of the manual control valve to release the load through said rst conduit, a cylinder, aspring-loaded piston therein, and a fluid connection between the cylinder and that part of the first conduit disposed between the check vvalve -and motor.

JOSEPH A. FRISCHMANN.

REFERENCES CITED The following references are of record in the -1 Adde June 20, 1 950 

